This invention generally relates to load bearing assemblies for elevator systems. More particularly, this invention relates to an arrangement for readily detecting localized strain in an elevator load bearing assembly.
Elevator systems typically include a cab and counterweight that are coupled together using an elongated load bearing member. Typical load bearing members include steel ropes and, more recently, synthetic ropes and multi-element ropes such as polymer coated, steel or synthetic cord reinforced belts. Synthetic ropes and polymer coated, synthetic cord reinforced belts are particularly attractive for elevator applications due to their greater strength-to-weight ratio compared with steel ropes or belts.
Inspecting a load bearing member in an elevator system has been accomplished in several ways. With conventional steel roping, a manual, visual inspection of the rope allows the technician to determine when particular strands of the steel rope are frayed, broken or otherwise worn. This inspection method is limited, however, to the exterior portions of the rope and does not provide any indication of the condition of interior strands of the rope. Additionally, a visual inspection method is somewhat difficult and time consuming and does not always permit complete inspection of the entire length of the load bearing arrangement.
There are similar limitations on using visual inspection techniques on newer ropes. For example, the polymer coated, polymer cord reinforced belts do not permit visual inspection because of the coating that is typically applied over the cords, which are made up of strands of polymer material. Several advances have been proposed for facilitating inspection of such load bearing arrangements. One example is shown in U.S. Pat. No. 5,834,942 where at least one carbon fiber is included in the load bearing member. An electric current is passed through the fiber. By measuring an electrical voltage across that fiber, a determination is made regarding the condition of the load bearing member. This proposal is limited, however, in that it does not provide any information regarding locations of maximum strain along the length of the load bearing member. Moreover, there is no way of guaranteeing that a loss of conductivity through the carbon fiber is directly correlated to strain or damage to the load bearing member. Another shortcoming of such an arrangement is that there is no qualitative information regarding degradation of the load bearing member over time.
There is a need for improved arrangements and methods for determining the condition of load bearing members in elevator assemblies. This invention provides a unique solution to that problem.
In general terms, this invention is a load bearing assembly for use in an elevator system. The inventive arrangement includes a plurality of non-ferromagnetic fibers arranged into at least one cord. At least one ferromagnetic element is associated with the cord. The ferromagnetic element is situated such that a physical characteristic of the ferromagnetic element changes responsive to strain on the non-ferromagnetic fibers. Such a change or changes in the ferromagnetic element can be detected. The ferromagnetic element, therefore, provides an indication of a condition of the assembly.
In one example, the ferromagnetic element breaks responsive to excessive strain on the non-ferromagnetic fibers. The breaks in the ferromagnetic element correspond to locations of the non-ferromagnetic elements that are strained. The ferromagnetic element preferably is chosen so that it breaks responsive to localized bending fatigue in the load bearing assembly.
A method of determining the condition of a load bearing assembly according to this invention includes arranging a ferromagnetic element in a selected relationship with a cord, which comprises a plurality of non-ferromagnetic fibers. The ferromagnetic element preferably is positioned in a selected relationship with the cord such that a physical characteristic of the ferromagnetic element changes responsive to localized strain on the non-ferromagnetic fibers. By determining a number of changes in the physical condition of the ferromagnetic element along the length of the assembly, a condition of the assembly is determined.
In one example, the method includes determining a number of breaks in the ferromagnetic element. By locating the breaks and comparing the number of breaks to predetermined selection criteria, the condition of the assembly can be determined to make a decision regarding the condition of the assembly to determine whether repair or replacement is needed.